Extraction of products from titanium-bearing minerals

ABSTRACT

The invention relates to a process for extracting metals and salts from titanium-bearing minerals such as perovskite. More particularly, although not exclusively, the invention relates to extracting titanium dioxide and optionally other compounds from melter slag derived from an iron-making process.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a § 371 national stage of PCT InternationalApplication No. PCT/NZ2015/050084, filed Jul. 8, 2015, claiming priorityof New Zealand Patent Applications Nos. NZ 627180, filed Jul. 8, 2014,NZ 627185, filed Jul. 8, 2014, and NZ 627187, filed Jul. 8, 2014 thecontent of each of which is hereby incorporated by reference into theapplication.

FIELD OF INVENTION

The invention relates to a process for extracting metals and salts fromtitanium-bearing minerals, and more particularly, although notexclusively, extracting titanium dioxide and optionally other compoundsfrom melter slag derived from an iron-making process.

BACKGROUND

There are numerous reserves of minerals from which valuable constituentscannot currently be recovered through means that are economicallyviable. The primary reason for this is that the grade of suchconstituents within the mineral reserves is too low, resulting in largeeffluent or by-product generation rates.

Melter slag, produced as a by-product during iron and steel makingprocesses, is one such mineral that contains low grades of commerciallyvaluable components, including titanium, aluminium and magnesium. Duringproduction of molten-pig iron, impurities are removed as melter slag.For some deposits, the slag is primarily perovskite (calcium titanate)and may typically contain between 20-40% titanium dioxide. Known melterslag extraction processes focus on extraction of titanium, due to ithaving the highest concentration within melter slag and the highestvalue. Titanium is a valuable pigment used in a number of commercialapplications such as the production of paints, paper, cement andpolymers. In melter slag, titanium is present in the form of perovskite,a titanium-calcium oxide crystalline structure from which recovery isdifficult. An example of a known method of extraction of titanium fromperovskite includes reacting perovskite with carbon at high temperaturesin an electrical furnace to produce titanium carbide. The titaniumcarbide is then chlorinated to produce titanium tetrachloride.Unfortunately, this method is energy intensive and the carbide producedhas an extremely high melting point, which creates handling problems inthe furnace.

Another method of extracting titanium from perovskite is that publishedin CA1,052,581. In this method, perovskite is treated by roasting at1200° C. in hydrogen sulphide gas. This is followed by leaching toremove calcium and iron sulphides which leaves the titanium as titaniumoxides. The disadvantages of this process are the high temperatures anduse of highly toxic gas.

Even minor improvements to a process for extracting saleable productsfrom minerals can have a significant impact on the efficiency, and moreparticularly, the commercial viability, of such a process. The methodsdetailed above are economically inefficient due to the high temperaturesused, and only titanium is extracted by these processes. It is an objectof the present invention to provide a method of extraction of productsfrom a titanium-bearing mineral, or to at least provide the public witha useful choice.

SUMMARY OF THE INVENTION

The present invention provides a response to the need in the art. Thepresent invention provides methods for extracting valuable products fromtitanium-bearing minerals.

In a first aspect, the invention provides a method of recoveringtitanium dioxide and at least one other product from a particulatematerial, said method comprising:

-   -   a. contacting the particulate material with sulphuric acid and        heating to form a sulphated mixture;    -   b. filtering the sulphated mixture to produce a filter cake and        a first permeate comprising sulphuric acid;    -   c. contacting the filter cake with water to form a sulphated        suspension comprising titanyl sulphate;    -   d. filtering the sulphated suspension to produce a permeate        comprising at least titanyl sulphate, and a retentate comprising        insoluble residue;    -   e. contacting the permeate comprising at least titanyl sulphate        with water to produce a hydrolysis liquor;    -   f. hydrolysing the titanyl sulphate; and    -   g. separating titanium dioxide hydrate from the hydrolysis        liquid,

wherein the at least one other product is selected from the groupconsisting of calcium sulphate, silica, aluminium sulphate or magnesiumsulphate.

In some embodiments, the titanium dioxide hydrate is separated byfiltering the hydrolysis liquor to produce a permeate, and a retentatecomprising titanium dioxide hydrate. In alternative embodiments, thetitanium dioxide hydrate is separated by centrifugation and collectionof the precipitate.

In particular embodiments, the insoluble residue comprises at least oneproduct selected from calcium sulphate and silica.

In particular embodiments, the invention provides a method of recoveringtitanium dioxide and at least one other product from a particulatematerial comprising greater than 8 m %, greater than 10 m %, greaterthan 15 m % greater than 20 m % or greater than 25 m % titanium dioxide,and greater than 10 m %, greater than 15 m % or greater than 20 m %silica. In other embodiments, the invention provides a method ofrecovering titanium dioxide and at least one other product from aparticulate material comprising greater than 8 m %, greater than 10 m %,greater than 15 m % greater than 20 m % or greater than 25 m % titaniumdioxide, and greater than 15 m %, greater than 20 m % or greater than 25m % calcium oxide.

In some embodiments, the invention provides a method of recoveringtitanium dioxide and at least one other product from a particulatematerial comprising greater than 8 m %, greater than 10 m %, greaterthan 15 m % greater than 20 m % or greater than 25 m % titanium dioxide,greater than 10 m %, greater than 15 m % or greater than 20 m % silica,and greater than 15 m %, greater than 20 m % or greater than 25 m %calcium oxide.

In some embodiments, the invention provides a method of recoveringtitanium dioxide and at least one other product from a particulatematerial comprising a ratio of titanium dioxide to calcium oxide(TiO₂:CaO) in the particulate matter of between 0.2 and 3.0, morepreferably between 0.3 and 2.5. In particular embodiments, the methodfurther comprises separation of calcium sulphate from the insolubleresidue using a floatation process.

In one embodiment, the invention provides a method of recoveringtitanium dioxide and aluminium sulphate from a particulate material,said method comprising:

-   -   a. contacting the particulate material with sulphuric acid and        heating to form a sulphated mixture;    -   b. filtering the sulphated mixture to produce a filter cake and        a first permeate comprising sulphuric acid;    -   c. contacting the filter cake with water to form a sulphated        suspension comprising titanyl sulphate;    -   d. filtering the sulphated suspension to produce a permeate        comprising at least titanyl sulphate, and a retentate comprising        insoluble residue;    -   e. contacting the permeate comprising at least titanyl sulphate        with water to produce a hydrolysis liquor;    -   f. hydrolysing the titanyl sulphate;    -   g. separating titanium dioxide hydrate from the hydrolysis        liquor to produce a permeate comprising aluminium sulphate, and        a retentate comprising titanium dioxide hydrate; and    -   h. precipitating aluminium sulphate from the permeate;

wherein step h. may be carried out after step d or after step g.

In particular embodiments, the method of the first aspect furthercomprises a step of precipitating aluminium sulphate after step g. Inone embodiment, the precipitation comprises the steps of:

-   -   cooling the permeate produced from the hydrolysis liquor to        produce a cooled liquor comprising precipitated aluminium        sulphate; and    -   filtering the cooled liquor to produce a retentate comprising        precipitated aluminium sulphate, and a permeate.

In particular embodiments, the method of the first aspect furthercomprises a step of precipitating aluminium sulphate after step g.wherein the particulate material comprises greater than 8 m %, greaterthan 10 m %, greater than 15 m % greater than 20 m % or greater than 25m % titanium dioxide, and greater than 10 m % or greater than 13 m %aluminium oxide.

In particular embodiments, the method of the first aspect furthercomprises a step of precipitating aluminium sulphate after step g.wherein the particulate material comprises a ratio of titanium dioxideto aluminium oxide (TiO₂:Al₂O₃) in the particulate matter ofapproximately 0.2 to 2.6, more preferably 0.25 to 2.1.

In particular embodiments, the method of the first aspect furthercomprises a step of precipitating aluminium sulphate prior to step f. Inone embodiment, the precipitation comprises:

-   -   cooling the permeate comprising at least titanyl sulphate to        produce a cooled liquor comprising precipitated aluminium        sulphate; and    -   filtering the cooled liquor comprising aluminium sulphate to        produce a retentate comprising precipitated aluminium sulphate,        and a permeate.

In particular embodiments the step of precipitating aluminium sulphatecomprises cooling the permeate to between 10° C. and 4° C. such that thealuminium sulphate crystallizes. In preferred embodiments, the permeatecomprising aluminium sulphate is cooled to approximately 5° C.

In particular embodiments, greater than 90% of the aluminium sulphatepresent in the sulphated suspension is recovered.

In particular embodiments, the method of the first aspect furthercomprises a step of precipitating magnesium sulphate from a permeatecomprising magnesium sulphate, wherein the permeate comprising magnesiumsulphate is either the hydrolysis liquor (after separation of titaniumdioxide hydrate), or the permeate produced following aluminium sulphateprecipitation.

In one embodiment, the invention provides a method of recoveringtitanium dioxide and magnesium sulphate from a particulate material,said method comprising:

-   -   a. contacting the particulate material with sulphuric acid and        heating to forma sulphated mixture;    -   b. filtering the sulphated mixture to produce a filter cake and        a first permeate comprising sulphuric acid;    -   c. contacting the filter cake with water to form a sulphated        suspension comprising titanyl sulphate;    -   d. filtering the sulphated suspension to produce a permeate        comprising at least titanyl sulphate, and a retentate comprising        insoluble residue;    -   e. contacting the permeate comprising at least titanyl sulphate        with water to produce a hydrolysis liquor;    -   f. hydrolysing the titanyl sulphate;    -   g. separating titanium dioxide hydrate from the hydrolysis        liquor to produce a permeate comprising magnesium sulphate, and        a retentate comprising titanium dioxide hydrate; and    -   h. precipitating magnesium sulphate from the permeate.

In one embodiment, the magnesium sulphate is precipitated by the stepsof:

-   -   increasing the acid concentration of a permeate comprising        magnesium sulphate to form an acidified liquor; and    -   filtering the acidified liquor to produce a retentate comprising        precipitated magnesium sulphate.

In particular embodiments, the acid concentration of the permeatecomprising magnesium sulphate is increased by the addition of sulphuricacid. Preferably the pH of the permeate comprising magnesium sulphate isreduced to less than approximately pH1 by the addition of sulphuricacid. In particular embodiments, the acid concentration of the permeatecomprising magnesium sulphate is increased by heating the permeate toremove water. Preferably heating is carried out at boiling point or at atemperature of greater than 130° C. Preferably heating is carried out toachieve a final acid concentration of 90%, or less than approximatelypH1.

In particular embodiments, the method of the first aspect furthercomprises a step of precipitating magnesium sulphate from a permeatecomprising magnesium sulphate, wherein the method includes the recoveryof titanium dioxide and magnesium sulphate product from a particulatematerial comprising greater than 8 m %, greater than 10 m %, greaterthan 15 m % greater than 20 m % or greater than 25 m % titanium dioxide,and greater than 7 m % or greater than 10 m % magnesium oxide.

In particular embodiments, the method of the first aspect furthercomprises a step of precipitating magnesium sulphate from a permeatecomprising magnesium sulphate, wherein the method includes the recoveryof titanium dioxide and magnesium sulphate product from a particulatematerial comprising a ratio of titanium dioxide to Magnesium oxide(TiO₂:MgO) in the particulate matter of approximately 0.5 to 3.0, morepreferably 0.8 to 2.8.

In one embodiment, the step of precipitating magnesium sulphatecomprises cooling the acidified liquor or a permeate comprisingmagnesium sulphate to a temperature where precipitation rate isincreased.

In another embodiment, the step of precipitating magnesium sulphatecomprises:

-   -   cooling the permeate comprising magnesium sulphate to produce a        cooled liquor comprising magnesium sulphate; and    -   filtering the cooled liquor comprising magnesium sulphate to        produce a retentate comprising precipitated magnesium sulphate,        and a permeate.

In preferred embodiments, the permeate comprising magnesium sulphate orthe acidified liquor is cooled to less than 4° C., between 0° C. and 4°C. or approximately 3° C.

In particular embodiments, greater than 90% of the magnesium sulphatepresent in the sulphated suspension is recovered following filtration.

In particular embodiments, the method of the first aspect furthercomprises:

-   -   precipitation of aluminium sulphate as described above, either        before or after hydrolysis; and    -   the retentate obtained from the sulphated suspension comprises        at least one of calcium sulphate and silica.

In particular embodiments, the method of the first aspect furthercomprises:

-   -   precipitation of magnesium sulphate as described above; and    -   the retentate obtained from the sulphated suspension comprises        at least one of calcium sulphate and silica.

In particular embodiments, the method of the first aspect furthercomprises:

-   -   precipitation of aluminium sulphate as described above, either        before or after hydrolysis; and    -   precipitation of magnesium sulphate as described above; and    -   the retentate obtained from the sulphated suspension comprises        at least one of calcium sulphate and silica.

In particular embodiments, the method of the first aspect furthercomprises:

-   -   precipitation of aluminium sulphate as described above, either        before or after hydrolysis; and    -   precipitation of magnesium sulphate as described above.

In one embodiment, the invention provides a method of recoveringtitanium dioxide, aluminium sulphate and magnesium sulphate from aparticulate material, said method comprising:

-   -   a. contacting the particulate material with sulphuric acid and        heating to form a sulphated mixture;    -   b. filtering the sulphated mixture to produce a filter cake and        a first permeate comprising sulphuric acid;    -   c. contacting the filter cake with water to form a sulphated        suspension comprising titanyl sulphate;    -   d. filtering the sulphated suspension to produce a permeate        comprising at least titanyl sulphate, and a retentate comprising        insoluble residue;    -   e. contacting the permeate comprising at least titanyl sulphate        with water to produce a hydrolysis liquor;    -   f. hydrolysing the titanyl sulphate;    -   g. separating titanium dioxide hydrate from the hydrolysis        liquor to produce a permeate comprising aluminium sulphate and        magnesium sulphate, and a retentate comprising titanium dioxide        hydrate;    -   h. precipitating aluminium sulphate from the permeate; and    -   i. precipitating magnesium sulphate from the permeate,

wherein step h. may be carried out after step d or after step g.

In particular embodiments of the first aspect, the particulate materialis iron slag or obtained from iron slag. In particular embodiments, theparticulate material is melter slag from an iron manufacturing process.In particular embodiments, the material is melter slag from a steelmanufacturing process.

In particular embodiments, the particulate material comprises i.titanium dioxide and at least one of the following components:

-   -   ii. silica;    -   iii. calcium oxide;    -   iv. aluminium oxide; and    -   v. magnesium oxide,

In particular embodiments, the method of the first aspect furthercomprises the step of grinding raw material comprising components i. tov. to form the particulate material of step a. In particularembodiments, the particulate material has a particle size of less than180 μm. In preferred embodiments, the particulate material has aparticle size from 10 to 180 μm, or from 40 to 110 μm. In particularembodiments, the particulate material has a particle size ofapproximately 30 μm, 45 μm, 60 μm, 70 μm, 80 μm, 90 μm, or 100 μm.

In particular embodiments, the particulate material comprises greaterthan 8 m % titanium dioxide. In other embodiments, the particulatematerial comprises greater than 10 m %, greater than 15 m %. greaterthan 20 m % or greater than 25 m % titanium dioxide.

In particular embodiments of the first aspect, the particulate materialof a. is contacted with 4-10 times its stoichiometric quantity ofsulphuric acid. In preferred embodiments, the particulate material of b.is contacted with 5-6, or approximately 6 times its stoichiometricquantity of sulphuric acid.

In particular embodiments, the sulphuric acid concentration is at least50 m %. In other embodiments, the acid concentration is at least 60 m %,70 m %, 80 m %, 90 m % or 98 m %.

In particular embodiments of the first aspect, the sulphated mixture isheated to achieve substantially complete sulphation of the oxides(particularly titanium dioxide/calcium titanate) present. In particularembodiments, the sulphated mixture is heated to at least 100° C.following contact with sulphuric acid. In preferred embodiments, themixture is heated to a maximum of approximately 250° C.

In particular embodiments, the sulphated mixture is heated to atemperature between 130° C. and 200° C., more preferably approximately150° C.-160° C. In particular embodiments, the mixture is heated for aheating period which allows substantially complete sulphation of thetitanium dioxide (and optionally other components) to occur. In oneembodiment, the heating period is between 15 minutes and one hour. Inparticular embodiments, the heating period is at least 30 minutes orapproximately 40 minutes. In particular embodiments, step a. occurs in areactor.

In particular embodiments of the first aspect, the step of filtering thesulphated mixture further comprises contacting the mixture withcompressed air. The temperature of the compressed air is preferablybelow 85° C. In particular embodiments, the temperature of thecompressed air is from 10° C. to 85° C. Preferably, the compressed airis from 30° C. to 85° C., or approximately 50° C., 60° C., 70° C. or 80°C.

In particular embodiments of the first aspect, the sulphuric acidremoved from the sulphated mixture is collected for re-use in step a.

In particular embodiments of the first aspect, the permeate comprisingat least titanyl sulphate is dehydrated using a membrane to produce aconcentrated permeate comprising at least titanyl sulphate in which themetal sulphates are concentrated.

In particular embodiments of the first aspect, the permeate comprisingat least titanyl sulphate is heated to remove water and increase thefree acidity. Preferably the permeate comprising at least titanylsulphate is heated to greater than 100° C., more preferably greater than130° C. and most preferably to greater than 160° C. or to boiling. Inparticular embodiments, the heated permeate comprising at least titanylsulphate is filtered to remove residual sulphuric acid and the resultingfilter cake (comprising precipitated titanyl sulphate and preferablyother precipitated sulphates) is contacted with water to obtain aconcentrated permeate comprising at least titanyl sulphate. Thispermeate may then be subjected to downstream process steps includinghydrolysis and optionally precipitation of aluminium/magnesium.

In particular embodiments, the free acidity of the hydrolysis liquor isfrom 8-25%. In other embodiments, the free acidity of the hydrolysisliquor is from 9-15%.

In particular embodiments of the first aspect, the hydrolysis liquor isheated to a temperature between 85 and 140° C., 80 and 140° C., 90° C.and 120° C., or between 105° C. to 110° C. Preferably the hydrolysisliquor is heated for a period such that substantially all of the titanylsulphate has reacted. Preferably, the heating period is from one hour tothree hours. More preferably from 90 minutes to two hours orapproximately 100 minutes. In particular embodiments, the solution isheated for about two hours at a temperature above 85° C. in order forhydrolysis to be completed.

In particular embodiments of the first aspect, the hydrolysis liquor iscontacted with water containing titanium dioxide particles. Preferablythe titanium dioxide particles are nanoparticles. Preferably, the amountof titanium dioxide particles added to the hydrolysis liquor is between2 m % and 30 m % of the mass of the titanium dioxide calculated to bepresent in the liquor. More preferably, between 2 m % and 15 m % andpreferably between 5 m % and 9 m %. Preferably, the particle size of thetitanium particles added to the liquor is from 2 nm to 10 nm, morepreferably 3 to 6 nm.

In particular embodiments of the first aspect, the method furthercomprises the step of sonicating the hydrolysis liquor to precipitatetitanium dioxide hydrate from the solution. Preferably, the hydrolysisliquor is sonicated in the absence of heating.

In one embodiment of the first aspect, the method further comprises thestep of calcining the titanium dioxide hydrate. Preferably calcining iscarried out at a temperature of between 800 and 1100° C., between 850°C. and 950° C., or between 890 and 910° C.

In a second aspect, the invention provides at least one product producedby the method of the first aspect, the product being selected from:

-   -   a. titanium dioxide;    -   b. silica;    -   c. calcium sulphate;    -   d. aluminium sulphate; or    -   e. magnesium sulphate.

In a third aspect, the invention provides a system for the recovery ofproducts from a particulate material, the system comprising:

-   -   a. a sulphation reactor adapted to receive and heat sulphuric        acid and particulate material comprising at least titanium        dioxide and produce a sulphated mixture;    -   b. a first filtration unit adapted to receive the sulphated        mixture and produce a first permeate comprising at least        sulphuric acid, and a filter cake comprising at least titanyl        sulphate;    -   c. a hydrolysis reactor adapted to receive a solution comprising        titanyl sulphate and heat said solution to produce a hydrolysis        liquor;    -   d. a separation unit adapted to receive the hydrolysis liquor        and separate titanium dioxide hydrate.

In particular embodiments of the third aspect, the separation unitcomprises a second filtration unit adapted to receive the hydrolysisliquor and produce a retentate comprising titanium dioxide. Inalternative embodiments the separation unit comprises a centrifugationunit adapted to separate the precipitated titanium dioxide hydrate.

In particular embodiments of the third aspect, the system furthercomprises at least one precipitation tank to facilitate precipitation ofaluminium sulphate or magnesium sulphate.

In particular embodiments, the particulate material further comprises atleast one of aluminium oxide, magnesium oxide, calcium oxide or silica.

In particular embodiments, the system further comprises at least onefurther filtration unit to facilitate separation of precipitatedaluminium sulphate or precipitated magnesium sulphate.

In a fourth aspect, the invention provides a method of recoveringproducts from a particulate material comprising the followingcomponents:

-   -   i. titanium dioxide;    -   ii. silica;    -   iii. calcium oxide;    -   iv. aluminium oxide; and    -   v. magnesium oxide,

said method comprising:

-   -   a. contacting the particulate material with sulphuric acid and        heating to form a sulphated mixture;    -   b. filtering the sulphated mixture to produce a filter cake and        a first permeate comprising sulphuric acid;    -   c. contacting the filter cake with water to form a sulphated        suspension comprising titanyl sulphate;    -   d. filtering the sulphated suspension to produce a retentate        comprising silica and calcium sulphate, and a permeate        comprising at least titanyl sulphate;    -   e. contacting the permeate comprising at least titanyl sulphate        with water to produce a hydrolysis liquor;    -   f. heating the hydrolysis liquor to hydrolyse the titanyl        sulphate;    -   g. separating titanium dioxide hydrate by filtering the        hydrolysis liquor to produce a retentate comprising titanium        dioxide hydrate and a permeate comprising aluminium sulphate and        magnesium sulphate;    -   h. precipitating aluminium sulphate and separating the        precipitate by filtering the liquor to produce a retentate        comprising precipitated aluminium sulphate, and a permeate        comprising magnesium sulphate;    -   i. precipitating magnesium sulphate and separating the        precipitate by filtering the liquor to produce a retentate        comprising precipitated magnesium sulphate.

Preferably, the step of precipitating aluminium sulphate in the methodof the fourth aspect comprises cooling the permeate comprising aluminiumsulphate and magnesium sulphate to produce a cooled liquor comprisingprecipitated aluminium sulphate; and filtering the cooled liquor toproduce a retentate comprising precipitated aluminium sulphate, and apermeate comprising magnesium sulphate.

Preferably, the step of precipitating magnesium sulphate in the methodof the fourth aspect comprises increasing the acid concentration of thepermeate comprising magnesium sulphate to form an acidified liquor; andfiltering the acidified liquor to produce a retentate comprisingprecipitated magnesium sulphate.

The invention also includes the parts, elements and features referred toor indicated in the specification of the application, individually orcollectively, in any or all combinations of two or more of said parts,elements or features, and where specific integers are mentioned hereinwhich have known equivalents in the art to which the invention relates,such known equivalents are deemed to be incorporated herein as ifindividually set forth.

Further aspects of the invention, which should be considered in all itsnovel aspects, will become apparent to those skilled in the art uponreading of the following description which provides at least one exampleof a practical application of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying drawings in which:

FIG. 1 shows a process flow diagram depicting an embodiment of theinvention.

FIG. 2 shows the chemical composition of different slag samples asdetailed in example 2.

FIG. 3 shows the chemical composition of different slag samples asmeasured by XRF in example 2 (for New Zealand and South Africa) andobtained from the literature in example 1 (for China and Russia).

FIG. 4a shows the amount of titanium dioxide measured in the permeatecomprising titanyl sulphate as measured by the titration method inexample 3. FIG. 4b shows the amount of titanium measured in the permeateas measured by the ICP-OES method in example 3.

FIG. 5 shows the ICP-OES measurements of titanium, calcium, aluminiumand magnesium in the permeate.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Definitions

Unless otherwise defined, the following terms as used throughout thisspecification are defined as follows: The term “product” or the like isintended to encompass minerals recovered from the raw material orparticulate material utilised in the described process. In particularembodiments, the products are titanium dioxide and at least one ofmagnesium, aluminium, calcium sulphate and silica, or theircorresponding salt (if applicable).

The term “particulate material” is intended to encompass a raw materialground to small particles to permit contact of the sulphuric acid witheach species of metal oxide. In particular embodiments, the particulatematerial has a particle size of less than 180 μm. In preferredembodiments, the particulate material has a particle size from 10 to 180μm, or from 40 to 110 μm. In particular embodiments, the particulatematerial has a particle size of approximately 30 μm, 45 μm, 60 μm, 70μm, 80 μm, 90 μm, or 100 μm.

The term “filter cake”, “cake” and the like refers to solid materialpresent on a filter or membrane following evacuation of liquid(typically acid) from the mixture. In particular embodiments, the filtercake comprises titanyl sulphate and at least one of magnesium sulphate,aluminium sulphate, calcium sulphate and silica.

The term “residue” is intended to encompass a solid material from whichwater soluble metal sulphates have been recovered following a leachingprocess. In particular embodiments, the residue comprises calciumsulphate (gypsum) and silica. In particular embodiments, the residuefurther comprises unreacted metal oxides.

The term “free acidity” refers to the portion of the total acidity thatexists in the form of acid, both ionized and un-ionized.

The term “reactor” includes any device consisting of one or more vesselsand/or towers or piping arrangements in which materials of the inventioncan be processed, mixed and/or heated. Examples of reactors of theinvention include continuous or batch infusion reactors.

The terms “mixture”, “solution” and “permeate” are used throughout thespecification, wherein the constituents alter depending on the stage ofthe process in which the terms are used. Where appropriate, the term“mixture” refers to a liquid with at least one solid substance insuspension. The term “solution” refers to an aqueous substance. The term“permeate” refers to a liquid obtained from a filtration process.Throughout this specification and any claims which follow, unless thecontext requires otherwise, the words “comprise”, “comprising”,“contain”, “containing” and the like, are to be construed in aninclusive sense as opposed to an exclusive sense, that is to say, in thesense of “including, but not limited to”.

“Perovskite” refers to a titanium-calcium oxide mineral composed ofcalcium titanate CaTiO₃. Perovskite typically has a cubic crystallinestructure although the term as used herein is intended to refer to anyform of calcium titanate. The terms perovskite and calcium titanate areused interchangeably.

“Fluid” refers to a material comprising one or more compounds that isable to flow. The fluid may also include one or more liquids, dissolvedsubstances, suspended substances or solid substances.

“Calcining” refers to a process whereby a substance is heated to a hightemperature but below the melting or fusing point, causing loss ofmoisture, reduction or oxidation, and the decomposition of carbonatesand other compounds.

“Gypsum” is CaSO₄.2H₂O. This term and “calcium sulphate” or CaSO₄ areused interchangeably throughout this specification.

The term “titanyl sulphate” is intended to cover other sulphate forms oftitanium which may also be present following sulphation. Those of skillin the art will appreciate such further titanium sulphate reactants.

“Titanium dioxide hydrate” as referred to herein is intended toencompass solutions containing both titanium dioxide and titaniumdioxide hydrate and any degree of hydration of the titanium dioxide. Itwill be appreciated by those of skill in the art that the product of thehydrolysis of titanyl sulphate will be a mixture of titanium dioxide andtitanium dioxide hydrate. Unless the context requires otherwise, wherethe term titanium dioxide is referred to herein, it will be understoodthat titanium dioxide hydrate may also be present in any proportion.Likewise, unless the context requires otherwise, where the term titaniumdioxide hydrate is referred to herein, it will be understood thattitanium dioxide may also be present in any proportion. Where aproportion, ratio or percentage of titanium dioxide in a feedstock isreferred to, it will be appreciated by a person skilled in the art thatthe actual form of the titanium dioxide may not be in a form appropriateto be purified. For example in perovskite, the form of the titaniumdioxide is predominantly as calcium titanate (CaTiO₃). Where analyticalresults referring to titanium dioxide are provided, those analyticalresults give the amount of titanium dioxide that may be bound with otherelements, for example in calcium titanate.

A “melter” refers to any apparatus appropriate to use high temperaturesto convert a solid mineral into a molten state. This term is alsointended to incorporate smelters and blast furnaces.

While the following description focuses on particular embodiments of theinvention, namely the production of titanium dioxide and at least one ofmagnesium sulphate, aluminium sulphate, calcium sulphate and silicausing melter slag from a steel manufacturing process as the primaryfeedstock, it should be appreciated that the invention may be applicableto production of alternative minerals and the use of alternativefeedstocks as will be known by persons of ordinary skill in the art towhich the invention relates.

A “system” comprises pipework and other features that would be typicallyemployed to enable the extraction of minerals from a particulate feed.By way of example, the “system” may include pressure valves, heatexchangers, filters, instrumentation (pressure sensors, flow sensors, pHsensors) and mixing tees (static mixers).

As discussed hereinbefore, the inventors have devised methods forrecovering valuable products from titanium-bearing minerals, such ascalcium titanate or perovskite, in a way that is commercially viable. Inparticular, the present invention provides methods for extraction oftitanium dioxide and at least one of magnesium sulphate, aluminiumsulphate, calcium sulphate or silica from melter slag, preferably froman iron-manufacturing process. In the case of melter slag, the processis surprisingly advantageous in that a number of high value minerals canby extracted from a material that is otherwise considered a wasteproduct. In addition the invention provides a means for extracting saidminerals that is economically efficient (e.g. is not energyintensive/does not require excessive heating steps) compared to methodsknown in the art.

In one embodiment, the inventors provide a method for the extraction ofthe products titanium dioxide, aluminium sulphate, magnesium sulphate,calcium sulphate and silica from a waste material using environmentallysustainable methods, including recycling extraction acids. Achieving thesuccessful extraction of these products provides commercial advantagesby enabling further value to be extracted from what is currently a wasteproduct (perovskite). Accordingly, in a further aspect, the inventionprovides a method of minimising waste from a titanium dioxide-containingproduct from an iron-making process. Minimising waste also hasenvironmental advantages including reduction of pollution and reductionof land use for iron slag.

FIG. 1 shows an embodiment of the invention in which minerals 1 areground in a grinder 2 to produce a particulate material. The particulatematerial is contacted with sulphuric acid from an acid holding tank 3 ina sulphation reactor 4 before being filtered in a first filtration unit5 to produce a permeate comprising sulphuric acid 6, and a filter cake7. The filter cake is contacted with water 8 to form a sulphatedsuspension in a reactor 9. The sulphated suspension is filtered in asecond filtration unit 10 to yield a retentate comprising insolubleresidue 11 and a permeate comprising at least titanyl sulphate. Water 12is added to the permeate which is then passed to a hydrolysis reactor13. Following hydrolysis, the fluid is filtered in a third filtrationunit 14 and precipitated material (predominantly titanium dioxidehydrate) is removed in a retentate 15. The permeate is passed to aprecipitation tank 16 in which aluminium sulphate is precipitated. Theprecipitate is then separated by filtration in a fourth filtration unit17. The retentate comprising aluminium sulphate is removed 18 and thepermeate passed to a second precipitation tank 19. Followingprecipitation of dissolved magnesium sulphate, the fluid is filtered ina fifth filtration unit 20 and a retentate comprising magnesium sulphate21 collected. The permeate (comprising predominantly acid) is collectedand may be recycled 22 through an acid regeneration plant 23.

Accordingly, in one aspect, the invention provides a method ofrecovering titanium dioxide and at least one other product from aparticulate material, said method comprising:

-   -   a. contacting the particulate material with sulphuric acid and        heating to form a sulphated mixture;    -   b. filtering the sulphated mixture to produce a filter cake and        a first permeate comprising sulphuric acid;    -   c. contacting the filter cake with water to form a sulphated        suspension comprising titanyl sulphate;    -   d. filtering the sulphated suspension to produce a permeate        comprising at least titanyl sulphate, and a retentate comprising        insoluble residue;    -   e. contacting the permeate comprising at least titanyl sulphate        with water to produce a hydrolysis liquor;    -   f. hydrolysing the titanyl sulphate; and    -   g. separating titanium dioxide hydrate from the hydrolysis        liquor,

wherein the at least one other product is selected from the groupconsisting of calcium sulphate, silica, aluminium sulphate or magnesiumsulphate.

Unless indicated otherwise, the order of steps described in the methodsdescribed herein is very much preferred and has been optimised by trialscarried out by the inventors to ensure that the process provides anefficient yield and an economically viable recovery method.

Feedstock

The feedstock used in the process is a titanium-bearing mineral.However, for ease of describing the process, the feedstock exemplifiedis melter slag from an iron manufacturing process. Melter slag istypically a by-product of the iron or steel manufacturing process,produced at the melter stage of the process. It is commonly used as anaggregate for road building and surfacing.

In particular embodiments, the material is iron slag. In particularembodiments, the material is melter slag from an iron manufacturingprocess. In particular embodiments, the material is melter slag from asteel manufacturing process. Melter slag is primarily comprised ofperovskite by mass (CaTiO₃) in a mixed metal oxide matrix. An example ofmelter slag constituents is provided below in Table 1, which details theconstituents of melter slag produced in New Zealand by NZ Steel's steelmanufacturing process.

TABLE 1 NZ Steel Melter Slag Constituent m % TiO₂ 32.1 Al₂O₃ 17.8 MgO13.3 CaO 15.9 SiO₂ 15.2 Fe₂O₃ 2.34 V₂O₅ 0.2

In order to prepare the feedstock for use in the process, the rawmaterial (e.g. melter slag) is preferably ground into a particulatematerial by any means known by persons of ordinary skill in the art. Therate and efficiency of mineral extraction from perovskite is dependenton the grind size. In particular embodiments, the material is ground toless than 180 μm. In preferred embodiments, the material is ground toapproximately 45 μm.

Accordingly, in particular embodiments, any of the methods of recoveryof products described herein may contain the further step of grindingraw material comprising one or more of the constituents in table 1 toform particulate material. In particular embodiments, the particulatematerial has a particle size of less than 180 μm. Having this particlesize provides for efficient sulphation of the oxides. However, using themethods described herein, the inventors have found that a smallerparticle size is only beneficial up to a point. If the particle size isreduced too far, for example to less than around 10 μm, the efficiencyof the filtration step to remove acid is reduced. It is believed thatthis reduction in efficiency is caused by the filter becoming blocked.Accordingly, in preferred embodiments, the particulate material has aparticle size from 10 to 180 μm, or from 40 to 110 μm. In particularembodiments, the particulate material has a particle size ofapproximately 30 μm, 45 μm, 60 μm, 741 m, 80 μm, 90 μm, or 100 μm.

A skilled person will appreciate the methods to achieve particle sizereduction. In one embodiment, the grinding is carried out in a ballmill.Particle size may be measured according to methods known to those ofskill in the art, for example laser diffraction.

The inventors have found that the relatively high level of titaniumdioxide and other materials in melter slag make it a suitable feedstockfor use in the recovery methods described herein. Accordingly, inparticular embodiments, the invention provides a method of recovering atleast one product from a particulate material comprising greater than 8m %, greater than 10 m %, greater than 15 m % greater than 20 m % orgreater than 25 m % titanium dioxide. Generally the higher the titaniumdioxide content, the more valuable the particulate material, and themore economically viable the process of recovery is. Accordingly, it ispreferably that the particulate material comprises at least than 15 m %titanium dioxide.

One of the key advantageous aspects of the methods of the inventiondescribed herein is the ability to recover more than one substantiallypurified product from the particulate material. By doing this, the wastefrom the process is reduced, and the products can be used or soldseparately. This increases the economic viability of the process andreduces land use for storage of the waste material. Accordingly, theinvention provides a method of recovery of titanium dioxide and at leastone other product selected from silica, calcium sulphate, aluminiumsulphate and magnesium sulphate.

The inventors have found that the order of the steps in the methoddescribed herein is an important factor in optimising yields of the mostvaluable materials. Early trials by the inventors (see example 3,samples 7, 8, 9 and 10) tested the aluminium sulphate precipitation stepprior to the titanium dioxide production and recovery step (i.e.hydrolysis). The yield of titanium dioxide when hydrolysis was carriedout after aluminium sulphate precipitation was lower than when carriedout before, probably due to co-precipitation of the two components.Accordingly, it is preferable to carry out titanium hydrolysis prior toaluminium sulphate precipitation. This is especially true where theratio of titanium dioxide to aluminium oxide is relatively low (seeexample 1 table 3). Additionally, the step of magnesium sulphateprecipitation is carried out after the precipitation of aluminiumsulphate and titanium dioxide. If magnesium sulphate precipitation iscarried out prior to recovery of either aluminium sulphate or titaniumdioxide, the co-precipitation of these components with magnesiumsulphate would reduce the economic viability of the method and reducethe purity with which the products could be obtained.

In particular embodiments, the invention provides a method of recoveringtitanium dioxide and at least one other product from a particulatematerial comprising greater than 8 m %, greater than 10 m %, greaterthan 15 m % greater than 20 m % or greater than 25 m % titanium dioxide,and greater than 10 m % or greater than 13 m % aluminium oxide. It isparticularly preferable to use a feedstock comprising at least 15 m %titanium dioxide and at least 13 m % aluminium oxide. The methodpreferably comprises carrying out the step of titanium hydrolysis priorto aluminium sulphate precipitation when the ratio of titanium dioxideto aluminium oxide (TiO₂:Al₂O₃) 0.2 to 2.6, more preferably 0.25 to 2.1.

Metal Sulphation

The particulate material is introduced to an appropriate reactor, suchas a fusion reactor, where it is combined with the desired amount ofsulphuric acid to form a sulphated mixture. Although it would generallybe thought of as being inefficient to use a large stoichiometric excessof reagents in a reaction, the inventors have found that a substantialexcess of sulphuric acid results in decreased viscosity of the sulphatedmixture. In particular, it was found that using a stoichiometric excessof two times or less results in a highly viscous mixture that isdifficult to pump. Accordingly, in particular embodiments, theparticulate material is contacted with greater than 2 times, andpreferably 4-10 times its stoichiometric quantity of sulphuric acid. Inpreferred embodiments, the particulate material is contacted withbetween 5 and 6 times, or approximately 6 times its stoichiometricquantity of sulphuric acid.

The key reactions relating to the processes and which are used by theinventors to determine the stoichiometric quantities of reactioncomponents are:CaTiO₃+2H₂SO₄→CaSO₄+TiOSO₄+2H₂OMgO+H₂SO₄→MgSO₄+H₂OAl₂O₃3H₂SO₄→Al₂(SO₄)₃+3H₂O

In particular embodiments, the sulphuric acid is introduced to asulphation reactor in the form of a concentrated acid solution, whereinthe particulate material is contacted with the acid solution to form anaqueous sulphated mixture. The inventors have found that if the acidstrength is too low (i.e. the amount of H₂SO₄ molecules by mass in theacid solution is too low), the reaction will fail to proceed, or willproceed at a rate that is too low to be economically viable.Accordingly, in particular embodiments, the sulphuric acid concentrationis at least 50 m %. A low acid concentration also affects the overalltitanium dioxide yield. Therefore the strength of the acid is preferablygreater than 70%, preferably 90%. In other embodiments, the acidconcentration is at least 60 m %, 70 m %, 80 m %, 90 m % or 98 m %.

In particular embodiments of the first aspect, the sulphated mixture isheated to achieve substantially complete sulphation of the oxides(particularly titanium dioxide/calcium titanate) present. In particularembodiments, the sulphated mixture is heated to at least 100° C.following contact with sulphuric acid. In preferred embodiments, themixture is heated to at least 200° C., preferably 250° C., in thesulphation reactor. The inventors have found that using a temperature ofover 250° C. is generally undesirable due to the apparatus constraintsof using very hot acid. Preferably, the temperature is between 130° C.and 200° C., more preferably approximately 150° C.-160° C.

In particular embodiments, preheated air or steam is introduced to thereactor, preferably through the bottom of the reactor. The air/steam isallowed to rise through the mixture in order to heat the mixture to thepoint where reaction commences. The purpose of this step is to decreasethe reaction time of the metal oxides converting to sulphates, and toevaporate the water as it is evolved, so as to maintain a high freeacidity. High free acidity is desired so that the sulphate saltsprecipitate, and can be filtered afterwards.

In particular embodiments, the sulphated mixture is heated such thatsubstantially complete sulphation of the calcium titanate/titaniumdioxide occurs. During heating, the viscosity of the mixture increasesas a function of the liquid content decreasing as the evolved waterevaporates. In particular embodiments, the mixture is heated for aheating period which allows substantially complete sulphation of theoxides (in particular calcium titanate/titanium dioxide) to occur. Inone embodiment, the heating period is at between 15 minutes and onehour. In particular embodiments, the heating period is at least 30minutes or approximately 40 minutes.

In particular embodiments, following the heating step, the mixture isfurther dehydrated using a membrane in order to increase the freeacidity of the mixture. In particular embodiments, the free acidity ofthe mixture exceeds 70% following dehydration.

It will be appreciated by those of skill in the art that heating of amixture may be achieved in any appropriate way. In one embodiment, oneor more of the components of the mixture may be pre-heated and the heattransferred to the mixture during mixing. References to “heating” of amixture herein are intended to encompass heating of one or more of thecomponents of that mixture prior to mixing.

Leaching

The sulphated mixture is next subjected to a first filtration step(otherwise known as leaching) in order to remove the sulphuric acid.Accordingly, the method of recovering products from a particulatematerial comprises the step of filtering the sulphated mixture in asuitable filtration unit to produce a filter cake and a permeatecomprising sulphuric acid. The inventors found during trials that ahigher acid content in the filter cake had an inhibitory effect on thedownstream process steps including hydrolysis and precipitation of metalsulphates. Accordingly, the step of acid recovery using a firstfiltration unit was introduced. This had the effect of reducing acidconcentration and provided unexpected efficiency increases of downstreamprocess steps including hydrolysis and precipitation i.e. increasedproduct yield.

Those of skill in the art will understand that any appropriatefiltration unit (filter) may be used for this purpose and exemplaryfiltration units will be known to them. In particular embodiments, thefiltration unit comprises a filter press. In one embodiment, thefiltration unit is assisted by a differential pressure gradient acrossthe filter. Preferably, the pressure differential is at least 1 bar. Inparticular embodiments, the mixture is circulated through a filtrationunit which permits acids to pass through, while a solid filter cake iscollected on the surface of the filter. In particular embodiments, thepressure differential across the filter is from 2 to 10 bar. Preferably,the pressure differential is approximately 6 bar. Using a filter cake isparticularly advantageous to achieve maximum acid extraction from thesulphated mixture. At this stage, the filter cake is comprised oftitanyl sulphate and at least one of magnesium sulphate, aluminiumsulphate, calcium sulphate or silica.

It is desirable to reduce the acid content of the filter cake as much aspossible. Preferably, the moisture content of the filter cake is reducedto less than 30%, more preferably less than 20%, or between 15 and 20%.The remaining liquid in the filter cake is largely acid. In particularembodiments, this first filtration step further comprises contacting thefilter cake with compressed air. The compressed air acts as an agitatorto evacuate acid from the filter and filter cake, and dries the filtercake further. The temperature of the compressed air is preferably below85° C. to prevent the premature hydrolysis of titanyl sulphate. Inparticular embodiments, the temperature of the compressed air is from10° C. to 85° C. Although the compressed air is expected to assist withdrying the filter cake at any temperature, the inventors have found thatusing a heated compressed air stream assists in maintaining thetemperature of the filter cake and the subsequent sulphated suspension.Accordingly, it is preferable that the compressed air is from 30° C. to85° C., or approximately 50° C., 60° C., 70° C. or 80° C. If thetemperature of the compressed air is too low (i.e. lower than 35° C.),the viscosity of the sulphated suspension is increased which candetrimentally affect fluid flow.

Sulphuric acid recovered from the mixture is preferably passed to anacid regeneration plant. The collected sulphuric acid may thenoptionally be reused in the metal sulphation step described previously,wherein recycle/of the sulphuric acid provides an economic andenvironmental advantage. In particular embodiments, the sulphuric acidis processed prior to being recycled for use in the metal sulphationstep.

The filter cake remaining on the filter now has a minimal acid content.Water is circulated through the filter cake in order to dissolve thesoluble salts from the filter cake. Preferably, the filter cake iswashed on the filter and water is passed through the filter.Alternatively, the filter cake is washed with water and the solutiondoes not pass through the filter. Optionally, the filter cake is removedand washed in a separate vessel. In situ washing (i.e. on the filter)reduces the need for an extra tank. Preferably, the filter cake isagitated using vibration or mechanical agitation during washing.Preferably, the temperature of the filter cake during washing is lessthan 80° C. If higher temperatures are used, the inventors have foundthat partial or complete hydrolysis of the titanyl sulphate occurs thusreducing downstream titanium dioxide yield. The water may be obtainedfrom any appropriate source. This step produces a solution comprisingtitanyl sulphate and at least one of magnesium sulphate and aluminiumsulphate. In particular embodiments, an insoluble residue remains on thefilter comprising calcium sulphate and silica. The solution comprisingtitanyl sulphate and at least one of magnesium sulphate and aluminiumsulphate is optionally passed to a membrane that dehydrates the solutionto produce a substantially concentrated solution of the metal sulphates.Concentration using the membrane may be by known membrane concentrationmethods including reverse osmosis.

The method of recovering products further comprises the step offiltering the sulphated suspension to produce a retentate comprising aninsoluble residue and a permeate comprising at least titanyl sulphate.In particular embodiments, the insoluble residue of the retentatecomprises silica and calcium sulphate. In particular embodiments, thepermeate comprises titanyl sulphate, aluminium sulphate and magnesiumsulphate.

Silica/Calcium Sulphate Separation

The inventors have found that the perovskite product produced frommelter slag often has a high amount of silica and calcium oxide present.These components are relatively low value and are often viewed asproblematic waste products that contaminate compositions containinghigher value materials such as titanium dioxide. However, throughextensive trials, the inventors have found that these components can beextracted in a substantially purified form as silica and calciumsulphate. Both products have use in industry, for example in theproduction of tyres and in the production of gypsum for buildingmaterials respectively. The inventors have found that sulphation of thecalcium oxide and removal as an insoluble residue prior to titaniumsulphate hydrolysis provides a particularly efficient and cost-effectivemethod of recovery of these components. In addition, where theparticulate material also contains quantities of at least one ofaluminium oxide and magnesium oxide, removal of the insoluble residuecomprising silica and calcium sulphate enables the recovery ofsubstantially pure titanium dioxide, and at least one of aluminiumsulphate and magnesium sulphate in later method steps. Overall, thesesteps and their order contribute to providing an inventive,cost-effective and industrially efficient method of recovering saidproducts with minimal waste.

In particular embodiments, the invention provides a method of recoveringtitanium dioxide and at least one other product from a particulatematerial comprising greater than 8 m %, greater than 10 m %, greaterthan 15 m % greater than 20 m % or greater than 25 m % titanium dioxide,and greater than 10 m %, greater than 15 m % or greater than 20 m %silica. In other embodiments, the invention provides a method ofrecovering titanium dioxide and at least one other product from aparticulate material comprising greater than 8 m %, greater than 10 m %,greater than 15 m % greater than 20 m % or greater than 25 m % titaniumdioxide, and greater than 15 m %, greater than 20 m % or greater than 25m % calcium oxide.

In some embodiments, the invention provides a method of recoveringtitanium dioxide and at least one other product from a particulatematerial comprising greater than 8 m %, greater than 10 m %, greaterthan 15 m % greater than 20 m % or greater than 25 m % titanium dioxide,greater than 10 m %, greater than 15 m % or greater than 20 m % silica,and greater than 15 m %, greater than 20 m % or greater than 25 m %calcium oxide.

Where the method comprises a step of recovering calcium sulphate and/orsilica, the insoluble residue may be processed to obtain these products.This residue is typically comprised of calcium sulphate, resulting fromthe cleavage of calcium titanate and the sulphation of calcium oxide,and silica. Quantities of unreacted metal oxides are typically presentalso, as a result of being encapsulated by a refractory material.

In one embodiment the insoluble residue of the retentate from thefiltration of the sulphated suspension step is passed to a floatationtank and at least one of calcium sulphate and silica is separatedaccording to known methods.

In one aspect of the invention, there is provided a method of recoveringproducts from a raw material containing perovskite, silica, aluminiumoxide and magnesium oxide, said method comprising:

a) grinding a material comprising perovskite, silica, aluminium oxideand magnesium oxide to produce a particulate material;

b) contacting the particulate material with sulphuric acid to form amixture containing titanyl sulphate, gypsum, silica, aluminium sulphateand magnesium sulphate;

c) filtering the mixture to remove the sulphuric acid;

d) contacting the mixture with water to dissolve the mixture andseparating the mixture using filtration to produce a solution comprisingtitanyl sulphate, aluminium sulphate and magnesium sulphate and aresidue comprising gypsum and silica;

e) cooling the solution to a temperature at which aluminium sulphatecrystallizes and recovering the resulting crystallized aluminiumsulphate;

f) precipitating the solution to produce titanium dioxide;

g) cooling the remaining solution to a temperature at which magnesiumsulphate crystallizes and recovering the crystallized magnesiumsulphate; and

h) calcining the titanium dioxide to remove residual acid and water toproduce substantially pure titanium dioxide.

Due to the difference in density between calcium sulphate and silica,and the hydrophilic nature of silica, calcium sulphate can be separatedand recovered from silica using a floatation process. In particularembodiments, calcium sulphate is recovered from the residue using afroth floatation process. In particular embodiments, the residue isground and/or cleaned prior to being subjected to a froth floatationprocess. In particular embodiments, the residue is subjected to apre-floatation step prior to the floatation process in order to recoverunreacted metal oxides. In particular embodiments, the residue issubjected to a post-floatation step following the floatation process inorder to recover unreacted metal oxides. The pre/post-floatation steppreferably comprises a floatation process using xanthates and/orhydroxamates to scavenge unreacted metal oxides. The pre/post-floatationstep may also be used to recover sulphates that were not dissolvedduring leaching.

In alternative embodiments, the calcium sulphate may be recovered fromthe insoluble residue by precipitation methods known to those of skillin the art.

Concentration of Permeate Comprising Titanyl Sulphate

A low free acidity is desirable for the titanium hydrolysis reaction toproceed efficiently. The free acidity of the liquor following leaching(i.e. the first permeate) or aluminium precipitation/crystallisation isgenerally too high to permit direct application of the liquor. Sinceacid is produced in the hydrolysis reaction, the inventors have foundthat it is desirable to minimise acid flow-through from the earliersulphation step. Doing this minimises equipment constraints and costsaround using highly concentrated acids.

The inventors found that an effective way to minimise acid flow-throughto the hydrolysis reaction is to first increase free acidity by removingwater from the liquor, then precipitate the metal sulphates and separatethem from the acid. In particular embodiments, the free acidity of thepermeate comprising titanyl sulphate and optionally at least one ofmagnesium sulphate and aluminium sulphate is first raised such that themetal sulphates precipitate and are more easily separated from the acid.In particular embodiments, the free acidity is raised by heating thesolution to a temperature at which the water evaporates. Preferably thepermeate comprising titanyl sulphate is heated to greater than 100° C.,more preferably greater than 130° C. and most preferably to greater than160° C. or to boiling point. Since the liquor contains a highconcentration of acid, the boiling point is approximately 160° C. Inalternative embodiments, the free acidity is raised by contacting thesolution with a membrane capable of dehydrating the solution, preferablyto remove substantially all water.

Once the free acidity of the solution has been raised, the solution isfiltered in order to remove substantially all acids and produce a filtercake on the surface of the filter. Following filtration, water iscirculated through the filter in order to dissolve the soluble saltsfrom the filter cake. This step is similar in nature to the leachingstep described previously, and produces a reduced-acid permeatecomprising titanyl sulphate and optionally at least one of magnesiumsulphate and aluminium sulphate. In this embodiment, the permeate isfiltered to remove residual acids and the resulting filter cake iscontacted with water to obtain a concentrated permeate comprising atleast titanyl sulphate.

Titanium Sulphate Hydrolysis

Titanium hydrolysis refers to the cleavage of sulphate from titanium.The reaction is as follows:TiOSO₄+H₂O>TiO₂+H₂SO₄

Experiments carried out by the inventors indicate that the optimal freeacidity of hydrolysis liquor ranges from 8-25%. Experiments haveindicated that at lower than 8% free acidity, the hydrolysis liquor isunstable which is undesirable. This is due to firstly, the hydrolysis oftitanyl sulphate can spontaneously occur at room temperature whilestanding. Secondly, the rate of hydrolysis is difficult to control.During hydrolysis the rate of hydrolysis is in part controlled by thefree acidity. If the rate of hydrolysis exceeds approximately 1%per-minute, new nucleation sites are generated in solution resulting ina wide size distribution of titanium dioxide aggregate, which isundesirable for pigment production. Accordingly, in some embodiments,the free acidity of the hydrolysis liquor comprises at least 8% freeacidity. A free acidity of greater than 25% is undesirable as thehydrolysis reaction does not proceed to completion even when heated andseeded. The hydrolysis of titanyl sulphate is under equilibrium control,as titanyl sulphate is hydrolysed free sulphate ions are produced henceincreasing free acidity in the hydrolysis liquor. According to the LeChatelier's principle, the concentration of the product (free acid)directly controls the forward rate of the reaction. Hence, a highstarting free acidity in the hydrolysis liquor can slow or completelystop the hydrolysis of titanyl sulphate. Accordingly, in someembodiments, the free acidity of the hydrolysis liquor comprises at lessthan 25% free acidity. In some embodiments, the free acidity of thehydrolysis liquor comprises between 8% and 25%. Within this specifiedrange, the hydrolysis of titanyl sulphate can proceed to completion in acontrolled manner resulting in hydrated titanium dioxide of aparticularly suitable size distribution for pigment production.

Having achieved a solution which has an appropriate level of freeacidity, and preferably in which the titanyl sulphate is concentrated,the step of hydrolysing the titanyl sulphate is initiated. Hydrolysiscomprises adding water to the permeate comprising titanyl sulphate (andoptionally at least one of magnesium sulphate and aluminium sulphate) toproduce a hydrolysis liquor and heating the hydrolysis liquor.Hydrolysis is carried out in a hydrolysis reactor appropriate to containthe reactions described herein. Preferably the hydrolysis liquor isheated to a temperature between 80 and 140° C., between 85 and 140° C.or between 85 and 120° C. The inventors have found that a minimumactivation energy for the hydrolysis reaction must be achieved byheating the liquor. In a particular embodiment, the hydrolysis liquor isheated to between 90° C. and 120° C. The inventors have found that aparticularly efficient temperature which initiates the reaction quicklywhile maintaining energy efficiency is from 105° C. to 110° C.

Preferably the hydrolysis liquor is heated for a period such thatsubstantially all of the titanyl sulphate has reacted. A skilled personwill be able to determine when all of the titanyl sulphate has reacted.In particular embodiments, the heating period is from one hour to threehours. More preferably from 90 minutes to two hours or approximately 100minutes. In particular embodiments, the solution is heated for about twohours at a temperature above 85° C. in order for hydrolysis to becompleted.

In particular embodiments, the hydrolysis process comprises contactingthe solution with water containing titanium dioxide or rutile andheating the solution to a temperature between 85 to 120° C. In preferredembodiments, titanium dioxide particles or nanoparticles, also referredto as seed particles, or nuclei, are added to the hydrolysis liquor. Thetitanium dioxide particles act as nucleating sites for crystallization,so as to achieve uniform particle formation. The titanium dioxideparticles may be added to the hydrolysis liquor or the water added toform said liquor. The titanium dioxide particles may be added and thehydrolysis liquor heated to any of the temperature ranges describedherein for hydrolysis. Preferably, the amount of titanium dioxideparticles added to the hydrolysis liquor is between 1 m % and 30 m % ofthe mass of the titanium dioxide calculated to be present in the liquor.More preferably, between 2 m % and 15 m % and preferably between 5 m %and 8 m %. Preferably, the particle size of the titanium particles addedto the liquor is from 2 nm to 10 nm, more preferably 3 to 6 nm orapproximately 5 nm. Titanium dioxide particles may be anatase, orobtained therefrom.

Separation of the hydrated titanium dioxide may be achieved by methodsknown to those of skill in the art. In particular embodiments,separation is carried out in a separation unit adapted to receive thehydrolysis liquor and separate titanium dioxide hydrate.

In particular embodiments, the separation unit comprises a secondfiltration unit adapted to receive the hydrolysis liquor and produce aretentate comprising titanium dioxide hydrate. In alternativeembodiments the separation unit comprises a centrifugation unit adaptedto separate the precipitated titanium dioxide hydrate.

In an alternative embodiment to the hydrolysis process described above,the hydrolysis liquor may instead be subjected to a sonication processin order to precipitate titanium dioxide hydrate from the solution. Inthis embodiment, the bulk fluid requires less heating or does notrequire heating.

Preferably, the step of separation of the titanium dioxide hydrate maybe carried out by filtering the hydrolysis liquor to Produce a permeate,and a retentate comprising titanium dioxide hydrate. In alternativeembodiments, the titanium dioxide is removed by centrifugation andcollection of the precipitate.

Filtration of the hydrolysis liquor is carried out in a suitablefiltration unit in order to recover the hydrated titanium dioxide. Inpreferred embodiments, the hydrolysis liquor remains heated to a maximumof approximately 80° C. in order to keep the titanium dioxide particleslarge enough to be captured by the filtering medium. The permeatepreferably comprises aluminium sulphate and magnesium sulphate.

The titanium dioxide recovered from the hydrolysis or sonication processmay be calcined (heated) in an oxidative environment by passing heatedair through the product, which removes any residual sulphuric acid andwater. In preferred embodiments, the titanium dioxide is heated to 950°C. in a reactor for about an hour. In other embodiments, the heatingperiod is from 30 minutes to two hours. In particular embodiments,calcining is carried out at a temperature of between 800 and 1050° C.,between 850° C. and 950° C., or between 890 and 910° C. The recoveredsulphuric acid can be reused in the sulphation step described earlier.In order to obtain a finished titanium dioxide product, the calcinedtitanium dioxide is milled, coated and washed. Such processes will beknown to those of skill in the art.

Aluminium Sulphate Recovery

Aluminium sulphate is precipitated from the liquor at an appropriatestage. The inventors have found that a higher yield of titanium dioxidecan be achieved by carrying out aluminium sulphate precipitation afterhydrolysis and titanium dioxide removal (see example 3, samples 7, 8, 9and 10). It is believed that if aluminium sulphate precipitation iscarried out before hydrolysis, some titanyl sulphate is co-precipitatedwith the aluminium sulphate thus reducing TiO₂ yield.

In one embodiment, aluminium sulphate is precipitated from the permeatecomprising titanyl sulphate. In another embodiment, aluminium sulphateis precipitated from the permeate comprising magnesium sulphate andaluminium sulphate. These permeates are typically obtained followingsulphation and removal of insoluble residue. Alternatively, if thealuminium sulphate is not required to be separated from the insolubleresidue, this step of aluminium sulphate precipitation may be carriedout before removal of the insoluble residue.

The process of aluminium sulphate precipitation preferably comprisescooling the permeate to a temperature at which aluminium sulphateprecipitates and crystallizes. In particular embodiments, the solutionis cooled in the same vessel in which the previous filtration stepoccurred. In alternative embodiments, the solution is passed to aseparate tank for cooling.

The crystallized aluminium sulphate is recovered from the solution byany method known to those skilled in the art. The precipitation andrecovery step can be carried out on liquors containing aluminiumsulphate, for example those produced by the methods described in example3. Filtration is particularly preferred. In particular embodiments, >90%of the aluminium sulphate present in the solution is recovered duringthis stage. In particular embodiments, the solution is cooled to between10 and 4° C. such that the aluminium sulphate crystallizes. In preferredembodiments, the solution is cooled to approximately 5° C.

In particular embodiments, the invention provides a method of recoveringat least one product from a particulate material comprising greater than8 m %, greater than 10 m %, greater than 15 m % greater than 20 m % orgreater than 25 m % titanium dioxide, and greater than 10 m % or greaterthan 13 m % aluminium oxide. The inventors have found that the methodprovides an economically viable method of recovery of such componentswhen the feedstock meets these component proportions.

Examples 1 and 2 show the deduction of component ratios in particularfeedstocks. In particular embodiments, the invention provides a methodof recovering titanium dioxide and aluminium sulphate product from aparticulate material comprising a ratio of titanium dioxide to aluminiumoxide (TiO₂:Al₂O₃) in the particulate matter of approximately 0.2 to2.6, more preferably 0.25 to 2.1. In this embodiment, the inventors havefound that the method steps provide particularly economically viablerecovery of titanium dioxide and aluminium sulphate. The titaniumhydrolysis step being carried out prior to aluminium sulphateprecipitation is particularly preferred at this ratio range. Further,where magnesium sulphate precipitation is also carried out, the titaniumhydrolysis step being carried out prior to aluminium sulphateprecipitation, which in turn is carried out before magnesium sulphateprecipitation is particularly preferred at this ratio range.

In a particular embodiment of the invention, there is provided a methodof recovering products from a raw material containing perovskite andaluminium oxide, said method comprising:

a) grinding a material comprising perovskite and aluminium oxide toproduce a particulate material;

b) contacting the particulate material with sulphuric acid to form amixture containing titanyl sulphate and aluminium sulphate;

c) filtering the mixture to remove the sulphuric acid;

d) contacting the mixture with water to dissolve the mixture andseparating the mixture using filtration to produce a solution comprisingtitanyl sulphate and aluminium sulphate;

e) cooling the solution to a temperature at which aluminium sulphatecrystallizes and recovering the resulting crystallized aluminiumsulphate;

f) precipitating the solution to produce titanium dioxide; and

g) calcining the titanium dioxide to remove residual acid and water toproduce substantially pure titanium dioxide.

Magnesium Sulphate Recovery

The solution remaining after subjection to the hydrolysis or sonicationprocess, and optionally removal of aluminium sulphate, typicallycomprises magnesium sulphate that can also be recovered. The inventorshave found that it is preferable to recover magnesium sulphate afterrecovery of other products because the purity of the resultant magnesiumsulphate precipitate is increased if the other components have beenremoved prior. This is because the methods described below toprecipitate magnesium sulphate would also precipitate aluminiumsulphate, titanyl sulphate and other components. If the magnesiumsulphate precipitation was not carried out after recovery of the othercomponents, the precipitated mixture would be difficult anduneconomically viable to separate to yield substantially purecomponents. The resultant lack of value in the mixture increases theprobability that it will be disposed of in an uncontrolled andunregulated manner, thus causing environmental degradation.

The precipitation and recovery step can be carried out on liquorscontaining magnesium sulphate, for example those produced by the methodsdescribed in example 3.

In particular embodiments, the method of recovering products comprisesthe step of increasing the acid concentration of the permeate comprisingmagnesium sulphate to form an acidified liquor comprising precipitatedmagnesium sulphate. The increased acidity causes the magnesium sulphateto precipitate. The method preferably further comprises filtering theacidified liquor in to produce a retentate comprising precipitatedmagnesium sulphate.

In particular embodiments, the acid concentration of the permeatecomprising magnesium sulphate is increased by the addition of sulphuricacid. Preferably the pH of the permeate comprising magnesium sulphate isreduced to less than approximately pH1 by the addition of sulphuricacid.

In particular embodiments, the acid concentration of the permeatecomprising magnesium sulphate is increased by heating the permeate toremove water. Preferably heating is carried out at boiling point or at atemperature of greater than 130° C.

The inventors have also found that it is preferable to carry outmagnesium sulphate precipitation after aluminium sulphate precipitation.The lower precipitation temperature of magnesium sulphate results inaluminium sulphate precipitating first during cooling of a solutioncomprising both dissolved aluminium sulphate and magnesium sulphate.Accordingly, it is preferable to carry out magnesium sulphateprecipitation after aluminium sulphate precipitation. In particularembodiments, the invention provides a method of recovering at least oneproduct from a particulate material comprising greater than 8 m %,greater than 10 m %, greater than 15 m % greater than 20 m % or greaterthan 25 m % titanium dioxide, and greater than 7 m % or greater than 10m % magnesium oxide. It is particularly preferable to use a feedstockcomprising at least 15 m % titanium dioxide and at least 10 m %magnesium oxide.

In some embodiments, the invention provides a method of recoveringtitanium dioxide and at least one other product from a particulatematerial comprising greater than 8 m %, greater than 10 m %, greaterthan 15 m % greater than 20 m % or greater than 25 m % titanium dioxide,and greater than 7 m % or greater than 10 m % magnesium oxide. It isparticularly preferable to use a feedstock comprising at least 15 m %titanium dioxide and at least 10 m % magnesium oxide.

The method preferably comprises carrying out the step of titaniumhydrolysis prior to magnesium sulphate precipitation. This enables theyield of titanium dioxide to be maximised and reduces co-precipitationlosses of titanium dioxide (or titanium sulphate) that could occur ifmagnesium sulphate precipitation was carried out prior to titaniumdioxide recovery. Examples 1 and 2 show the deduction of componentratios in particular feedstocks. The method preferably comprisescarrying out the step of titanium hydrolysis prior to magnesium sulphateprecipitation when the ratio of titanium dioxide to magnesium oxide(TiO₂:MgO) in the particulate matter is from 0.5 to 3.0, more preferably0.8 to 2.8.

In some embodiments, the invention provides a method of recoveringtitanium dioxide and at least one other product from a particulatematerial comprising greater than 8 m %, greater than 10 m %, greaterthan 15 m % greater than 20 m % or greater than 25 m % titanium dioxide,and greater than 7 m % or greater than 10 m % magnesium oxide, andgreater 10 m % or greater than 13 m % aluminium oxide. It isparticularly preferable to use a feedstock comprising at least 15 m %titanium dioxide, at least 13 m % aluminium dioxide and at least 10 m %magnesium oxide.

In some embodiments, the invention provides a method of recoveringtitanium dioxide and at least one other product from a particulatematerial comprising greater than 8 m %, greater than 10 m %, greaterthan 15 m % greater than 20 m % or greater than 25 m % titanium dioxide,greater than 10 m %, greater than 15 m % or greater than 20 m % silica,greater than 15 m %, greater than 20 m % or greater than 25 m % calciumoxide and greater than 7 m % or greater than 10 m % magnesium oxide.

In some embodiments, the invention provides a method of recoveringtitanium dioxide and at least one other product from a particulatematerial comprising greater than 8 m %, greater than 10 m %, greaterthan 15 m % greater than 20 m % or greater than 25 m % titanium dioxide,greater than 10 m %, greater than 15 m % or greater than 20 m % silica,greater than 15 m %, greater than 20 m % or greater than 25 m % calciumoxide, greater than 10 m % or greater than 13 m % aluminium oxide andgreater than 7 m % or greater than 10 m % magnesium oxide.

In a particular embodiment, the invention provides a method ofrecovering titanium dioxide and at least one other product from aparticulate material comprising greater than 8 m % titanium dioxide,greater than 10 m % silica, greater than 15 m % calcium oxide, greaterthan 10 m % aluminium oxide and greater than 7 m % magnesium oxide. Inthis embodiment the method provides a commercially viable and usefulmethod for the extraction of these compounds from what was previouslyviewed as a waste material.

In an alternative embodiment, the invention provides a method ofrecovering titanium dioxide and at least one other product from aparticulate material comprising greater than 15 m % titanium dioxide,greater than 10 m % silica, greater than 15 m % calcium oxide, greaterthan 10 m % aluminium oxide and greater than 7 m % magnesium oxide.

In particular embodiments, the invention provides a method of recoveringtitanium dioxide and magnesium sulphate product from a particulatematerial comprising a ratio of titanium dioxide to magnesium oxide(TiO₂:MgO) in the particulate matter of approximately 0.5 to 3.0, morepreferably 0.8 to 2.8. In this embodiment, the inventors have found thatthe method steps provide particularly economically viable recovery oftitanium dioxide and magnesium sulphate. The titanium hydrolysis stepbeing carried out prior to magnesium sulphate precipitation isparticularly preferred at this ratio. Further, where aluminium sulphateprecipitation is also carried out, the titanium hydrolysis step beingcarried out prior to aluminium sulphate precipitation, which in turn iscarried out before magnesium sulphate precipitation is particularlypreferred at this ratio range.

In one embodiment, the inventors provide a method of recovering productsfrom a raw material containing perovskite and magnesium oxide, saidmethod comprising:

a) grinding a material comprising perovskite and magnesium oxide toproduce a particulate material;

b) contacting the particulate material with sulphuric acid to form amixture containing titanyl sulphate and magnesium sulphate;

c) filtering the mixture to remove the sulphuric acid;

d) contacting the mixture with water to dissolve the mixture andseparating the mixture using filtration to produce a solution comprisingtitanyl sulphate and magnesium sulphate;

e) precipitating the solution to produce titanium dioxide;

f) cooling the remaining solution to a temperature at which magnesiumsulphate crystallizes and recovering the crystallized magnesiumsulphate; and

g) calcining the titanium dioxide to remove residual acid and water toproduce substantially pure titanium dioxide.

In particular embodiments, the acidified liquor comprising magnesiumsulphate or a permeate comprising magnesium sulphate is cooled to atemperature at which magnesium sulphate crystallizes. In particularembodiments, the solution is cooled in the same reactor in which theprevious precipitation, hydrolysis process or sonication processoccurred. In alternative embodiments, the solution is passed to aseparate tank for cooling.

In particular embodiments, the permeate comprising magnesium sulphate orthe acidified liquor comprising magnesium sulphate is cooled to induceprecipitation/crystallisation of magnesium sulphate. In preferredembodiments, the permeate comprising magnesium sulphate or the acidifiedliquor is cooled to less than 4° C. or between 0° C. and 4° C., morepreferably approximately 3° C. In particular embodiments, greater than90% of the magnesium sulphate present in the acidified liquor or thepermeate comprising magnesium sulphate is recovered during filtration.The crystallized magnesium sulphate is recovered from the solution byany method known to those skilled in the art.

In addition, the systems or processes of the invention may optionallyinclude means for regulating and/or controlling other parameters toimprove overall efficiency of the process. One or more processors may beincorporated into the system to regulate and/or control particularparameters of the process. For example particular embodiments mayinclude determining means to monitor the composition of mixtures orsolutions. In addition, particular embodiments may include a means forcontrolling the delivery of a mixture or solution to particular stagesor elements within a particular system if the determining meansdetermines the mixture or solution has a composition suitable for aparticular stage.

In addition, it may be necessary to heat or cool particular systemcomponents or mixtures, solutions or additives prior to or during one ormore stages in the process. In such instances, known heating or coolingmeans may be used.

Furthermore, the system may include one or more pre/post treatment stepsto improve the operation or efficiency of a particular stage. Forexample, a pre-treatment step may include means for removing unwantedparticulate matter from the ground feedstock prior to the metalsulphation process. Other pre- or post-operations that may be conductedinclude separation of desired product(s) from particular stages. Theinvention has been described herein with reference to certain preferredembodiments, in order to enable the reader to practice the inventionwithout undue experimentation. Those skilled in the art will appreciatethat the invention can be practiced in a large number of variations andmodifications other than those specifically described. It is to beunderstood that the invention includes all such variations andmodifications. Furthermore, titles, headings, or the like are providedto aid the reader's comprehension of this document, and should not beread as limiting the scope of the present invention. The entiredisclosures of all applications, patents and publications cited hereinare herein incorporated by reference. More particularly, as will beappreciated by one of skill in the art, implementations of embodimentsof the invention may include one or more additional elements. Only thoseelements necessary to understand the invention in its various aspectsmay have been shown in a particular example or in the description.However, the scope of the invention is not limited to the embodimentsdescribed and includes methods including one or more additional stepsand/or one or more substituted steps, and/or and/or methods omitting oneor more steps.

The reference to any prior art in this specification is not, and shouldnot be taken as, an acknowledgement or any form of suggestion that thatprior art forms part of the common general knowledge in the field ofendeavour in any country.

EXAMPLES Example 1—Determination of Composition of Slag from DifferentSources

The composition of slag from steel manufacturing facilities wasobtained.

Results

TABLE 2 composition of raw material feedstock Component (m %) Slagsource TiO₂ SiO₂ CaO Al₂O₃ MgO Sum New Zealand 34.8 14.1 16.3 19.0 13.898.0 South Africa 28.2 16.5 16.6 13.6 14 99.2 China 1 21.5 15.55 24.614.11 7.65 83.84 China 2 16.03 24.94 32.12 14.89 7.47 96.02 Russia 9 2931 14.5 12 96.54

TABLE 3 ratio of feedstock components to titanium dioxide Componentratio Slag source TiO₂:Al₂O₃ TiO₂:MgO TiO₂:SiO₂ TiO₂:CaO New Zealand 1.82.5 2.5 2.1 South Africa 2.1 2.0 1.7 1.7 China 1 1.5 2.8 1.4 0.9 China 21.1 2.1 0.6 0.5 Russia 0.6 0.8 0.3 0.3

FIG. 3 shows the composition of the above slag samples measured by theinventors (for New Zealand) and obtained from the following literaturefor South Africa, China and Russia:

South Africa—Control of open slag bath furnaces at Highveld Steel andVanadium Ltd: development of operator guidance tables. Steinberg andPistorius, Ironmaking and Steelmaking, 2009, vol 36 no. 7.

China 1 and China 2-3rd International Symposium on High TemperatureMetallurgical Processing. Tao Jiang Jiann-Yang Hwang Patrick MassetOnuralp Yucel Rafael Padilla Guifeng Zhou—9 May 2012. John Wiley & Sons

Russia—Titania-containing slag processing method—RU 2295582

CONCLUSION

All five sources of slag for which data were obtained had varyingdegrees of metal oxides capable of extraction using the methodsdescribed herein.

Example 2

Materials and Methods

Six samples containing mixtures of titanium dioxide, aluminium oxide,magnesium oxide, silica and calcium oxide were analysed using x-rayfluorescence spectrometry. The mass percentage composition of thesesamples was determined and ratios of titanium dioxide to a secondcomponent calculated.

Results

TABLE 4 compositions and component ratios of samples measured usingx-ray fluorescence spectrometry Component (m %) Ratio Slag source TiO₂SiO₂ CaO Al₂O₃ MgO TIO₂:Al₂O₃ TiO₂:MgO TiO₂:SiO₂ TiO₂:CaO 1 -NZ-P112-Ti: Ca = 2.1 34.8 14.1 16.3 19.0 13.8 1.84 2.52 2.47 2.14 2 -ZA-P114-Ti: Al = 2.1 30.3 19.3 15.8 15.0 12.0 2.02 2.53 1.57 1.92 3 -L108-Ti: Al = 0.3 16.1 6.0 7.7 61.5 6.7 0.26 2.40 2.68 2.09 4 - L109-Ti:Ca = 0.2 15.3 6.0 58.1 8.9 7.7 1.72 1.98 2.55 0.26 5 - L110-Ti: Al = 0.315.9 6.0 7.7 61.7 6.7 0.26 2.38 2.65 2.06 6 - L111-Ti: Ca = 0.3 19.3 7.649.1 11.2 9.2 1.72 2.11 2.54 0.39

FIG. 2 shows the composition of samples 1-6.

CONCLUSION

Samples were obtained with a range of compositions. These compositionsare representative of a range of industrial slag compositions and corecomponent ratios.

Example 3—Sulphation of Slag Comprising Titanium Dioxide

Materials and Methods

Sulphation and Hydrolysis (Samples 1 and 3 to 6)

-   -   1. 100 g samples of particulate material corresponding to        samples 1 to 6 from example 2 were transferred to a 1 L round        bottom flask;    -   2. 1 kg of 98% sulphuric acid was added;    -   3. the mixture was heated, stirred and held at a temperature of        200° C. for around 4 hours;    -   4. the resultant sulphated mixture was cooled and filtered        through a 46K filter cloth under vacuum;    -   5. the filter cake was transferred to a 1 L conical flask and        washed with 1:1 stoichiometry (mass) of RO water for 2 hours at        70° C.;    -   6. the mixture was stirred and for approximately 15 hours then        filtered through a 46K filter cloth under vacuum to produce a        permeate comprising at least titanyl sulphate;    -   7. the permeate (comprising at least titanyl sulphate) was        sampled and the samples subjected to inductively coupled plasma        atomic emission spectroscopy (ICP-OES) analysis for titanium,        calcium, aluminium and magnesium. The titanium dioxide content        of the samples was also analysed using lab titration;    -   8. the permeate comprising at least titanyl sulphate was        transferred to a 1 L round bottom flask and diluted 1:2        stoichiometry (mass) with RO water (3× dilution) to produce a        hydrolysis liquor;    -   9. the hydrolysis liquor was heated to boiling point        (approximately 104° C.) for 5 hours with stirring to hydrolyse        the titanyl sulphate;    -   10. the precipitated titanium dioxide was separated from the        hydrolysis liquor by centrifugation at 8000 rpm for 20 minutes        to pellet the precipitated hydrated titanium dioxide;    -   11. The remaining hydrolysis liquor was analysed using ICP-OES        to determine the amount of remaining titanium, aluminium and        magnesium in mg/L. A yield of titanium dioxide was calculated        from this value. The amount of aluminium and magnesium remaining        (as sulphate salts) for downstream extraction was also measured.

The free acidity of the reaction liquor was measured at the followingstages:

-   -   a. the filtered acid removed following the initial filtration;    -   b. the permeate comprising titanyl sulphate from the second        filtration; and    -   c. the hydrolysis liquor remaining after the hydrated titanium        dioxide had been precipitated and centrifuged.

Sulphation and Hydrolysis Method (Sample 2)

-   -   1. A 1.5 kg sample of sample 2-(P114) (see example 2) was ground        to form a particulate material of a particulate size of        approximately x μm using a ball mill;    -   2. 8 L of 98% sulphuric acid was added;    -   3. the mixture was heated and held at a temperature of 200° C.        for around 4.5 hours while under 2 bar pressure and stirred at        300 rpm;    -   4. the resultant sulphated mixture was cooled and filtered        through a 46K filter cloth at 50° C.;    -   5. the filtration was carried out at 5 bar pressure and blown        with compressed air for 30-40 mins;    -   6. the permeate (comprising at least titanyl sulphate) was        sampled and the samples subjected to inductively coupled plasma        atomic emission spectroscopy (ICP-OES) analysis for titanium,        calcium, aluminium and magnesium. The titanium dioxide content        and free acidity of the samples was also analysed using lab        titration according to the methods described in example 3.    -   7. the filter cake was leached with 1:1 stoichiometry (mass) of        RO water for 2.5 hours at 70° C. i.e. 3028 g of filter cake was        leached with 3000 g of RO water, to, produce a hydrolysis        liquor;    -   8. the hydrolysis liquor was then filtered through a 46K filter        cloth for 15 mins at 1-3 bar and air blown for 20 mins;    -   9. The hydrolysis liquor was then transferred to a 3 L round        bottom flask and diluted 1:2 stoichiometry (mass) with RO water        (3× dilution);    -   10. this diluted liquor was then heated to boiling to hydrolyse        the titanyl sulphate for 5 hours with stirring;    -   11. the hydrated titanium dioxide was centrifuged out at 8000        rpm for 20 minutes to pellet the precipitated hydrated titanium        dioxide;    -   12. The remaining hydrolysis liquor was analysed using ICP-OES        to determine the amount of remaining titanium, aluminium and        magnesium. A yield of titanium dioxide was calculated from this        value. The amount of aluminium and magnesium remaining (as        sulphate salts) for downstream extraction was also measured.

Precipitation of Aluminium Sulphate

-   -   13. Following hydrolysis the acidity of the liquor comprising        aluminium sulphate was increased to around 40% (w/w) with 98%        sulphuric acid.    -   14. This high acidity liquor was then centrifuged at 8000 rpm        and 20° C. for 3 hours to precipitate out the aluminium sulphate        and pelletise it for separation.

Titration Method to Determine Concentration of Titanium Dioxide

-   -   1. Pipetted out approximately 1 mL of the sample into the 500 mL        Erlenmeyer flask and determined the exact mass of the sample.    -   2. Added 60 mL of 10% HCl, 20 mL of 98% H        ₂SO₄ and about 1.3 g of aluminium foil.    -   3. Once the reaction was complete allowed for some cooling to        occur. This was when some NaHCO3 was sucked back into the flask        and formed a buffering CO2 layer.    -   4. Added 6 drops of methylene blue indicator while the solution        was still warm.    -   5. Titrated against an acidified 0.1M Cerium sulphate standard.    -   6. The endpoint of the titration is when the colour changes from        pale yellow to pale green.

Determination of Free Acidity

-   -   1. Pipetted out approximately 1 mL of the sample into a 500 mL        Erlenmeyer flask and determined the exact mass of the sample.    -   2. Added 100 mL of RO water to the flask    -   3. Added 4 drops of the phenolphthalein indicator    -   4. Titrated against a standardised 1M NaOH solution.    -   5. The endpoint of the titration is when the colour changes from        colourless to a slight pink.

Results

Samples subjected to the sulphation method described above were analysedand the compositions of the permeate in table 5 were measured:

TABLE 5 analysis results of permeate produced following filtration Labtitration results Titanium Free Dioxide Acidity ICP-OES results (mg/L)Sample number (g/kg) (%) Titanium Calcium Aluminium Magnesium 1 -NZ-P112-Ti: Ca = 2.1 33.76 31.54 30379 159 13103 10429 2 - ZA-P114-Ti:Al = 2.1 39.15 29.47 37835 478 19492 18099 3 - L108-Ti: Al = 0.3 22.5332.44 18063 110 26012 6287 4 - L109-Ti: Ca = 0.2 16.64 31.06 11297 1445068 4799 5 - L110-Ti: Al = 0.3 20.66 32.97 15723 107 24542 5539 6 -L111-Ti: Ca = 0.3 24.29 29.07 19852 233 8341 8332

The free acidity of the permeate was in a range of 29% to 33%.

FIG. 4a shows the amount of titanium dioxide measured in the permeatecomprising titanyl sulphate as measured by the titration method. FIG. 4bshows the amount of titanium measured in the permeate as measured by theICP-OES method. It can be seen that the measurements obtained using thelab titration method closely correlate to the measurements obtainedusing the ICP-OES method. FIG. 5 shows the ICP-OES measurements oftitanium, calcium, aluminium and magnesium in the permeate.

TABLE 6 ICP-OES results showing titanium present in the permeatecomprising titanyl sulphate (prior to hydrolysis) and titanium remainingin the spent hydrolysis liquor (after precipitation of titanium dioxideand centrifugation/filtration to remove the precipitate). Titanium inTitanium in spent permeate hydrolysis Sample number (mg/L) liquor (mg/L)Yield (%) 1 - NZ-P112-Ti: Ca = 2.1 30379 1546 95 2 - ZA-P114-Ti: Al =2.1 37835 4199 89 3 - L108-Ti: Al = 0.3 18063 1612 91 4 - L109-Ti: Ca =0.2 11297 292 97 5 - L110-Ti: Al = 0.3 15723 1022 93 6 - L111-Ti: Ca =0.3 19852 1415 93

TABLE 7 ICP-OES results showing aluminium and magnesium present in thehydrolysis liquor following removal of titanium dioxide. ICP-OES results(spent hydrolysis liquor) (mg/L) Sample number Aluminium Magnesium 1 -NZ-P112-Ti: Ca = 2.1 5069 3126 2 - ZA-P114-Ti: Al = 2.1 3167 2821 3 -L108-Ti: Al = 0.3 6280 1552 4 - L109-Ti: Ca = 0.2 1250 1253 5 - L110-Ti:Al = 0.3 5362 1307 6 - L111-Ti: Ca = 0.3 2377 2124

TABLE 8 Free acidity of reaction liquor at specific reaction stages.Free acidity (%) Permeate comprising titanyl Hydrolysis Sample numberFiltered acid sulphate liquor 1 - NZ-P112-Ti: Ca = 2.1 85.53 31.54 10.72 - ZA-P114-Ti: Al = 2.1 90.85 29.47 9.52 3 - L108-Ti: Al = 0.3 85.2332.44 10.85 4 - L109-Ti: Ca = 0.2 86.73 31.06 10.03 5 - L110-Ti: Al =0.3 84.27 32.97 9.52 6 - L111-Ti: Ca = 0.3 83.98 29.07 9.34

In the instance where aluminium sulphate is precipitated first andfiltered out, there is a loss of titanyl sulphate to this materialstream. Table 9 describes the losses to the precipitated aluminiumsulphate due to hold-up of the titanyl sulphate in the aluminiumsulphate as it precipitates (occlusion)

TABLE 9 Equivalent titanium dioxide losses when extracting aluminiumsulphate prior to hydrolysis Lab titration results Mass CalculationsTitanium Free Mass of Mass of Loss of Dioxide Acidity Liquor TiO₂ TiO₂ %Sample number (g/kg) (%) (g) (g) (g) Loss 7 - L112-Ti: Al = 0.3 Leach16.11 27.81 678 10.92 Liquor 8 - L112-Ti: Al = 0.3 Post Al 14.01 38.43533 7.47 3.45 31.6 Sulphate Precipitation Liquor 9 - ZA-P114-Ti: Al =2.1 Leach 39.15 29.47 630 24.66 Liquor 10 - ZA-P114-Ti: Al = 2.1 Post29.05 35.22 588 17.08 7.58 30.7 Al Sulphate Precipitation Liquor

CONCLUSIONS

The ICP-OES results in table 5 show that substantial quantities oftitanium, aluminium and magnesium are dissolved and pass through thefilter substantially devoid of insoluble residues and other undesirableimpurities. The titanium, aluminium and magnesium in the permeate are inthe form of sulphate salts and can be separately precipitated accordingto the methods described herein.

The free acidity measurements indicate that the permeate comprisingtitanyl sulphate is in a range of 29% to 33%.

The amount of calcium in the ICP-OES analyses is very low indicatingthat the calcium oxide present in the original samples (see FIG. 2/3 andtable 4) is precipitated and removed as calcium sulphate during thefiltration step.

The yield measurements shown in table 6 indicate a high efficiencyextraction of titanium salts (89-97% efficiency. The yield measurementsalso indicate that the methods described herein are effective and highlyefficient for a range of particulate matter compositions and componentratios (see table 4 and FIG. 2).

Table 7 shows that there is a substantial quantity of aluminium andmagnesium present in the liquor following hydrolysis and removal oftitanium dioxide. These other components (present in the form ofsulphate salts) are available for extraction in later method stepprecipitations.

Table 8 shows that the free acidity of the samples filtered acid is veryhigh. The permeate comprising titanyl sulphate contains a reduced amountof free acid and the hydrolysis liquor contains approximately 10% freeacidity. Additional experiments carried out by the inventors indicatedthat if the free acidity of the hydrolysis liquor is greater than 25%,the hydrolysis reaction is energetically unfavourable and does notproceed, or does not proceed to completion. Additionally, the inventorshave found that it is preferable that the hydrolysis liquor contains afree acidity of greater than approximately 8% to enable completehydrolysis of the titanium sulphate to occur.

Table 9 shows that there are significant losses of equivalent titaniumdioxide that would otherwise be available for hydrolysis, in theinstance where aluminium sulphate is precipitated prior to hydrolysis.The losses are due in large part to titanyl sulphate being occluded inthe coarse aluminium sulphate crystals that form during precipitation.In developing the technique of hydrolysing titanyl sulphate to titaniumdioxide prior to aluminium sulphate precipitation, the inventors haveimproved the economic viability of the process.

A comparison of the two sulphation/hydrolysis methods used shows thatthey produce comparable results. In a commercial context, the secondmethod (used for sample 2) is generally preferable due to the higherthroughput available. Additionally, the inventors contemplate that in acommercial context, the centrifugation step would be replaced by analternative, higher throughput separation technique such as filtration.Those of skill in the art will appreciate that such separationtechniques may be used to obtain the products referred to herein fromthe liquor/permeate comprising said products.

Example 4—Recovery of Magnesium Sulphate

Materials and Methods

Extraction of Magnesium Sulphate

-   -   1. 1000 mL of the liquor is received from the hydrolysis        reaction (optionally following recovery of aluminium sulphate).        The liquor comprising magnesium sulphate and sulphuric acid is        heated to a temperature above 180° C. by placing in a heated,        stirred vessel.    -   2. As the liquor reaches boiling point at 180° C., the        concentration of the acid in solution will reach approximately        75%.    -   3. The liquor is held at 180° C. for 60 minutes    -   4. The magnesium sulphate in solution will precipitate as the        acid concentration rises    -   5. The liquor is allowed to cool to ambient temperature    -   6. The liquor and precipitate is filtered in a vacuum filter        with 46K cloth    -   7. The retentate is removed, dried and analysed with XRF to        determine composition    -   8. The permeate will be high concentration sulphuric acid. A        sample of this will be analysed for composition with ICP-OES or        ICP-MS technique.    -   9. A sample of the permeate will also be titrated for free        acidity

Example 5

This example describes a proposed method to achieve higher acidconcentration in a permeate comprising magnesium sulphate. This methoddehydrates the liquor thus decreasing pH. The higher sulphuric acidconcentration results in magnesium sulphate precipitating from thepermeate.

A permeate comprising magnesium sulphate is obtained from a method ofrecovering products from a particulate material as described in example3. The permeate is passed to a reverse osmosis unit comprising at leastone reverse osmosis membrane. The permeate is fed to the unit under apressure greater than the pressure on the other side of the membrane,for example 1.5 bar.

The retentate is collected and allowed to settle. Magnesium sulphateprecipitation occurs spontaneously or may be assisted by cooling oraddition of further acid. Precipitated magnesium sulphate is collectedvia filtration.

The invention claimed is:
 1. A method of recovering titanium dioxide,aluminium sulphate and magnesium sulphate from a particulate materialcomprising perovskite, said method comprising: a. contacting theparticulate material comprising perovskite with sulphuric acid andheating to a maximum of 250° C. to form a sulphated mixture; b.filtering the sulphated mixture to produce a filter cake and a firstpermeate comprising sulphuric acid; c. contacting the filter cake withwater to form a sulphated suspension comprising titanyl sulphate; d.filtering the sulphated suspension to produce a second permeatecomprising at least titanyl sulphate, and a retentate comprisinginsoluble residue comprising calcium sulphate; e. contacting the secondpermeate comprising at least titanyl sulphate with water to produce ahydrolysis liquor; and f. hydrolysing the titanyl sulphate; g.separating titanium dioxide hydrate from the hydrolysis liquor toproduce a third permeate comprising aluminium sulphate and magnesiumsulphate, and a retentate comprising titanium dioxide hydrate, torecover the titanium dioxide hydrate; and h. precipitating aluminiumsulphate from the second permeate or from the third permeate, to recoverthe aluminium sulphate; i. precipitating magnesium sulphate from thethird permeate, to recover the magnesium sulphate; wherein step h may becarried out after step d when using the second permeate or after step gwhen using the third permeate.
 2. The method of claim 1 wherein theinsoluble residue further comprises silica.
 3. The method of claim 1wherein step h of precipitating aluminium sulphate comprises: a. coolingthe second permeate from step d or the third permeate from step g toproduce a cooled liquor comprising precipitated aluminium sulphate; andb. filtering the cooled liquor to produce a retentate comprisingprecipitated aluminium sulphate, and a fourth permeate.
 4. The method ofclaim 3 wherein step h of precipitating aluminium sulphate comprisescooling the third permeate to between 10° C. and 4° C.
 5. The method ofclaim 1 wherein the precipitation of magnesium sulphate comprises thesteps of: a. increasing the acid concentration of the third permeatecomprising magnesium sulphate to form an acidified liquor; and b.filtering the acidified liquor to produce a retentate comprisingprecipitated magnesium sulphate.
 6. The method as claimed in claim 5wherein the acid concentration of the third permeate comprisingmagnesium sulphate is increased by the addition of sulphuric acid. 7.The method as claimed in claim 5 wherein the pH of the third permeatecomprising magnesium sulphate is reduced to less than pH1 by theaddition of sulphuric acid.
 8. The method as claimed in claim 5 whereinthe acid concentration of the third permeate comprising magnesiumsulphate is increased by heating the third permeate to remove water. 9.The method of claim 1 wherein the particulate material comprises greaterthan 8% by mass titanium dioxide, greater than 10% by mass aluminiumoxide and greater than 10% by mass magnesium oxide.
 10. The method ofclaim 1 wherein the particulate material comprises a ratio of titaniumdioxide to aluminium oxide (TiO₂:Al₂O₃) of approximately 0.2 to 2.6. 11.The method of claim 1 wherein the particulate material comprises a ratioof titanium dioxide to magnesium oxide (TiO₂:MgO) of approximately0.5:3.0.
 12. The method of claim 1 wherein step i of precipitatingmagnesium sulphate comprises: a. cooling the third permeate comprisingmagnesium sulphate, to produce a cooled liquor comprising magnesiumsulphate; and b. filtering the cooled liquor comprising magnesiumsulphate to produce a retentate comprising precipitated magnesiumsulphate, and a fourth permeate.
 13. The method of claim 12 wherein thethird permeate is cooled to between 0° C. and 4° C.
 14. The method ofclaim 1 wherein the particulate material is selected from the groupconsisting of iron slag, melter slag, obtained from iron slag, obtainedfrom melter slag, obtained from an iron manufacturing process, andobtained from a steel manufacturing process.
 15. The method of claim 1wherein the particulate material has a particle size between 10 to 180μm.
 16. The method of claim 1 wherein the particulate material iscontacted with 4-10 times its stoichiometric quantity of sulphuric acid.17. The method of claim 1 wherein the step of filtering the sulphatedmixture further comprises contacting the mixture with compressed air.18. The method of claim 1 wherein the second permeate comprising atleast titanyl sulphate is heated to remove water and increase the freeacidity.
 19. The method of claim 1 wherein the hydrolysis liquor iscontacted with water containing titanium dioxide particles.
 20. Themethod of claim 1 wherein step i of precipitating magnesium sulphatecomprises: a. increasing the acid concentration of the third permeatecomprising magnesium sulphate, to form an acidified liquor; b. coolingthe acidified liquor to produce a cooled liquor comprising magnesiumsulphate; and b. filtering the cooled liquor comprising magnesiumsulphate to produce a retentate comprising precipitated magnesiumsulphate, and a fourth permeate.
 21. The method of claim 1 wherein thecalcium sulphate is recovered.
 22. The method of claim 2 wherein thesilica is recovered.
 23. A method of recovering titanium dioxide,aluminium sulphate and magnesium sulphate from a particulate materialcomprising perovskite, said method comprising: a. contacting theparticulate material comprising perovskite with sulphuric acid andheating to a maximum of 250° C. to form a sulphated mixture; b.filtering the sulphated mixture to produce a filter cake and a firstpermeate comprising sulphuric acid; c. contacting the filter cake withwater to form a sulphated suspension comprising titanyl sulphate; d.filtering the sulphated suspension to produce a second permeatecomprising at least titanyl sulphate, and a retentate comprisinginsoluble residue comprising calcium sulphate; e. contacting the secondpermeate comprising at least titanyl sulphate with water, to produce ahydrolysis liquor; and f. hydrolysing the titanyl sulphate; g.separating titanium dioxide hydrate from the hydrolysis liquor, toproduce a third permeate comprising aluminium sulphate and magnesiumsulphate, and a retentate comprising titanium dioxide hydrate, torecover the titanium dioxide hydrade; and h. precipitating aluminiumsulphate from the second permeate or from the third permeate, to recoverthe aluminium sulphate; i. precipitating magnesium sulphate from thethird permeate, to recover the magnesium sulphate; wherein step h may becarried out after step d when using the second permeate or after step gwhen using the third permeate; and wherein the method further includescalcining the titanium dioxide hydrate to recover titanium dioxide.